Abstract
Periprosthetic fractures involving the femoral meta/diaphysis can be treated in various fashions. The overall incidence of those fractures after primary total knee arthroplasties (TKA) ranges from 0.3 to 2.5%, however, can increase above 30% in revision TKA, especially in older patients with poorer bone quality. Various classifications suggest treatment algorithms. However, they are not followed consequently. Revision arthroplasty becomes always necessary if the implant becomes loose. Next, it should be considered in case of an unhappy TKA prior to the fracture rather than going for an osteosynthesis. Coverage of the associated segmental bone loss in combination with proximal fixation, can be achieved in either cemented or non-cemented techniques, with or without the combination of osteosynthetic fracture stabilization. Severe destruction of the metaphyseal bone, often does not allow adequate implant fixation for the revision implant and often does not allow proper anatomic alignment. In addition the destruction might include loss of integrity of the collaterals. Consequently standard or even revision implants might not be appropriate. Although first reports about partial distal femoral replacement are available since the 1960´s, larger case series or technical reports are rare within the literature and limited to some specialised centers. Most series are reported by oncologic centers, with necessary larger osseous resections of the distal femur.
The implantation of any mega prosthesis system requires meticulous planning, especially to calculate the appropriate leg length of the implant and resulting leg length. After implant and maybe cement removal, non-structural bone might be resected. Trial insertion is important due to the variation of overall muscle tension and recreation of the former joint line. So far very few companies offer yet such a complete, modular system which might also be expanded to a total femur solution. Furthermore it should allow the implantation of either a cemented or uncemented diaphyseal fixation. In general, the fracture should be well bridged with a longer stem in place. At least 3 cm to 5 cm of intact diaphysis away to the fracture site is required for stable fixation for both cemented and cementless stems. Application of allograft struts and cables maximises the biomechanical integrity of the fracture zone to promote fracture repair and implant fixation. Modular bridging systems do allow centimeter wise adaption distally, to the knee joint. Consequently in modern systems fully hinged or rotational hinge knee systems can be coupled, and adjusted accordingly to the patellar tracking and joint line. Fixation of the tibial component can be achieved in uncemented and cemented techniques. We still prefer the latter.
Although a reliable and relatively quick technique, frequent complications for all mega systems have been described. These usually include infections, rotational alignment and loosening of the femoral fixation or subsequent proximal femoral fractures. Infections usually can be related to large soft tissue compromise or extensive exposure or longer procedure times. Thus implantation of such reconstruction systems should be reserved to specialised centers, with adequate facilities experience, in order to minimise complications rates and optimise patients function postoperative.
